The present invention relates to a switched power supply converter that comprises at least one switching element with which the transfer of energy between the input and the output of the power supply converter is governed.
The switching element is controlled so that its duty cycle is at all times a function of the value of the output voltage, whereby the power supply converter offers a high efficiency over a universal range of input voltages.
The switched power supply converter is of special, but not exclusive application in telecommunications systems, which are fed from voltage sources of 38 to 380 V.
A switched power supply converter which has a switching element whose duty cycle is variable and which receives a broad range of input voltages has been described, for example, in the U.S. Pat. No. 5,856,739 granted to A. Trica, incorporated in the present patent application by reference.
The switched converter, implemented according to a buck topology, comprises a switching element that has a high switching frequency and a variable duty cycle, an internal control current loop, an external control voltage loop and a control circuit that controls the duty cycle of the switching element as a function of the current loop and of the voltage loop.
The power supply converter accepts a broad range of input voltages of up to four times the output voltage. The converter is capable of working in voltage ranges that include voltage values supplied from batteries and from alternating current supply sources. However it is incapable of working with higher ranges, for example 10:1, and providing power levels equal to or greater than 100 W.
In the U.S. Pat. No. 5,006,782 granted to Pelly, teaches a two or more buck converter circuits are cascaded in such a manner that the output of one serves as the input to the next, with the input voltage to each succeeding buck converter stage being reduced in magnitude.
The first stage of the buck converter containing a first switching transistor having an adjustable duty cycle to produce a nominally fixed output voltage. The output voltage of the first stage is lower than the minimum input voltage but is higher than the desired final output voltage of the cascaded buck converter. The output voltage of the first stage forms the input voltage of the second stage. The switching transistor in the second stage has a nominally fixed duty cycle sufficient to reduce its input voltage, which corresponds to the output voltage of the first stage, to some fixed output voltage for the second stage.
The first stage is designed to reduce input voltage of 450 volts to some constant value 80 volts. This is accomplished by continually adjusting the duty cycle of the switching transistor in the first stage.
Unfortunately, when the input voltage is outside of the range between 450 volts and 80 volts, first stage does not teaches how is adjusting the duty cycle of the switching transistor in the first stage.
It has become necessary to develop a switched power supply converter that accepts a universal range of input voltages, which includes the voltage values supplied normally by the batteries of telecommunications systems, and guarantees for all of them the provision of a constant and regulated voltage at its output, so that the converter offers a high efficiency over the entire range of input voltages.
To overcome the problems outlined above a switched power supply converter for a broad range of input voltages is proposed which is of ideal dimensions and electrical operating characteristics for supplying telecommunications systems with electrical power equal to o greater than 100 W.
An object of the switched power supply converter of the invention is to provide a converter that works with a very broad voltage range, for example 38 to 380 V (10:1), with simple overall operation and high overall performance. The power supply converter is implemented by means of two conversion stages connected in cascade. Both stages are implemented by means of straightforward, highly efficient conversion topologies.
A further object is that both conversion stages have a control circuit for regulating respectively their output voltage, the regulation processes being independent of each other.
The control circuit for the first stage regulates the duty cycle of a switching element of the first stage in the event that the input voltage lies within a predetermined range of input voltages, and when the input voltage is outside said range, the duty cycle is set to a value so that the output voltage of the first stage is proportional to the input voltage. As a consequence, the range of input voltages of the second stage is less than the range of input voltages of the first stage. Then, it is possible to optimise the operation of the components of the second stage, in particular for boosting its efficiency.
The switched power supply converter for broad range of input voltages of the invention is divided into a first stage that converts a first voltage supplied from a voltage source into a second voltage by means of a first switching element; a second stage receives the second voltage and transforms it into a third DC voltage.
A control circuit controls the duty cycle of the first switching element so that the duty cycle varies between a first limit of the duty cycle and a second limit of the duty cycle when the first voltage is within a predetermined range of voltage values. The control circuit sets the duty cycle to the first limit of the duty cycle or to the second limit of the duty cycle in the event that the first voltage lies outside the predetermined range of voltage values. over the entire range of input voltages.
To overcome the problems outlined above a switched power supply converter for a broad range of input voltages is proposed which is of ideal dimensions and electrical operating characteristics for supplying telecommunications systems with electrical power equal to or greater than 100 W.
An object of the switched power supply converter of the invention is to provide a converter that works with a very broad voltage range, for example 38 to 380 V (10:1), with simple overall operation and high overall performance. The power supply converter is implemented by means of two conversion stages connected in cascade. Both stages are implemented by means of straightforward, highly efficient conversion topologies.
A further object is that both conversion stages have a control circuit for regulating respectively their output voltage, the regulation processes being independent of each other.
The control circuit for the first stage regulates the duty cycle of a switching element of the first stage in the event that the input voltage lies within a predetermined range of input voltages, and when the input voltage is outside said range, the duty cycle is set to a value so that the output voltage of the first stage is proportional to the input voltage. As a consequence, the range of input voltages of the second stage is less than the range of input voltages of the first stage. Then, it is possible to optimise the operation of the components of the second stage, in particular for boosting its efficiency.
The switched power supply converter for broad range of input voltages of the invention is divided into a first stage that converts a first voltage supplied from a voltage source into a second voltage by means of a first switching element; a second stage receives the second voltage and transforms it into a third DC voltage.
A control circuit controls the duty cycle of the first switching element so that the duty cycle varies between a first limit of the duty cycle and a second limit of the duty cycle when the first voltage is within a predetermined range of voltage values. The control circuit sets the duty cycle to the first limit of the duty cycle or to the second limit of the duty cycle in the event that the first voltage lies outside the predetermined range of voltage values.